This invention relates to molding of silicone, and more particularly, to a method and apparatus for molding and curing silicone.
Presently, silicone is molded using a press which holds a heated top and bottom mold cavity while the liquid silicone is injected into the mold using a pump. After the silicone is cured under heat, the press is lifted, the mold is separated and the molded silicone part is removed. The typical mold comprises a top mold plate which contains a mold cavity and a runner cavity. The silicone is injected under pressure into the runner cavity where it flows into the mold cavity. When the silicone cures, the silicone remaining in the runner cavity, referred to as runner silicone, must then be separated from the remaining silicone and the runner cavity.
One problem with the conventional techniques for molding silicone is that the hot mold cannot normally be handled manually. This problem has prevented the development of a molding and curing system which can be used to mold silicone onto a substrate such as fabric.
There exists a need to facilitate an apparatus which will allow silicone to be molded onto a substrate such as fabric while minimizing the propensity for the operator to be burned by a hot mold plate. There also exists a need to facilitate the prompt removal of runner silicone during the molding process.
The aforementioned needs may be achieved and the aforementioned problems may be solved, using the apparatus for curing and injecting silicone constructed in accordance with the principles of the present invention.
In accordance with the invention, the apparatus for molding and curing silicone includes a press, one or more injection nozzles operatively engaged to the press, a liquid cooled manifold plate disposed to cool the nozzles, a heatable top platen having one or more receptacles therein to receive the nozzles therein, and a mold plate having a mold cavity therein. The top platen is kept at a constant elevated temperature. The mold plate and top platen are also oriented for placement in an injecting position to allow the top platen to contact the mold plate while the nozzles are inserted into the nozzle receptacles of the top platen wherein silicone is injected into the mold plate through the nozzles and into the mold cavity.
The mold plate and top platen are oriented for placement in a curing position so that the heated top platen contacts the mold plate to allow silicone injected within the mold plate to cure. When in the curing position, the nozzle is outside of the receptacle of the top platen and the top platen is uncooled by the manifold plate.
The top platen and mold plate are also oriented for placement in a home position. In this position, the nozzles are located outside of the receptacles of the top platen, and the mold plate is uncontacted by the top platen.
The mold plate is typically located on a bottom platen when in the injecting position. The bottom platen is kept at a constant elevated temperature.
The mold plate includes a runner cavity which is in silicone flow relationship with the mold cavity when the nozzles are placed in silicone flow relationship with the runner cavity and the top platen and mold plate are in the injecting position.
A runner remover may be used to remove runner silicone from within the mold cavity. The runner remover may include a plurality of fingers which are placed within the runner cavity when the mold plate and top platen are in the injection position. The fingers are disposed to lift the runner silicone out of the runner cavity when the top platen and mold plate are placed in the home position. This may be accomplished by orienting the fingers so that they are slidably engaged to the top platen. The fingers may be spring loaded into the top platen. The runner remover may further include means for disengaging the silicone runner from the fingers, such as a plurality of tines.
The top platen of the apparatus may be linearly translatable relative to the nozzles and the manifold plate. The mold plate may also be linearly translatable relative to the top platen and the nozzles. The apparatus may also include a means for aligning the nozzles, the top platen, and the mold plate, with each other. The means for aligning may include at least one pin, and preferably four pins, axially aligned through the manifold plate, the top platen and the mold plate.
The apparatus may further include a first biasing means between the top platen and the manifold plate, and a second biasing means between the top platen and the mold plate. The first biasing means may include one or more springs located between the manifold plate and the top platen. Preferably, four springs may be located therebetween. The second biasing means may include one or more springs located between the top platen and the mold plate. Preferably, four springs may be located therebetween. The biasing means biases the top platen and mold plate in the home or open position.
The apparatus may further include a means for holding a substrate upon the bottom platen. The means may include at least one pressure activated push rod. The push rod may be operatively connected to a fluid, such as air cylinder.
The invention also includes a method of molding and curing silicone. The method involves aligning one or more injection nozzles into nozzle receptacles of a top platen, cooling the nozzles using liquid, placing the nozzles relative to a mold plate using a press and injecting silicone into a mold cavity within the mold plate under pressure, curing the injected silicone by heating the top platen and contacting the mold plate with the heated top platen. The heating step may include removing the nozzles from within the nozzle receptacles, and maintaining the heated top platen on the mold plate.
The nozzles may be located within a manifold plate and the cooling step may involve flowing cooling liquid into the manifold plate. The heated top platen may be lifted off of the mold plate after the silicone within the mold cavity has cured. The mold plate may include a runner cavity in silicone flow relationship to the mold cavity, and the method may further include removing runner silicone from the runner cavity. The silicone may be injected onto a substrate maintained in position on a heated bottom platen during the injection step. The substrate may be a fabric material, and the silicone may be injected and cured onto the fabric. The method may be performed using the apparatus of the present invention.